158 



ANIMAL STUDIES 



Fia. 97. An unattached crinoid (Anteclon). 

 half natural size. 



One- 



the power of locomotion. In some of the sea-cucumbers 

 five equidistant rows of tube-feet extend from, one end of 

 the body to the other, and the animal crawls worm-like, 

 upon any side that happens to be down ; but certain spe- 

 cies living in the sand, 

 where tube - feet will 

 not work satisfactorily, 

 have lost all traces of 

 them, and creep like an 

 earthworm from place 

 to place. In all the 

 sea-cucumbers the feet, 

 situated near the mouth, 

 have been curiously 

 modified to form a cir- 

 clet of tentacles, which 

 range in form from 



highly branched to short and thick structures, and in func- 

 tion from respiratory organs and those of touch to con- 

 trivances for scooping up sand and conveying it to the 

 mouth. 



147. Food and digestive system. In the echinoderms the 

 body-wall is comparatively thin (Fig. 98), and encloses a 

 great space, the body-cavity, in which the digestive and re- 

 productive organs are contained. As the former in various 

 species is adapted for acting upon very different kinds of 

 food, it shows many modifications ; but there are a few prin- 

 cipal types which may be briefly considered. 



In the starfishes the mouth enters almost directly into 

 the cardiac division of the stomach, a capacious, thin-walled 

 sac, much folded and packed away in the disk and bases of 

 the arms (Fig. 98, b). This in turn leads into the second 

 pyloric portion (), with thicker walls and dorsal, to the 

 first, from which a short intestine leads to the exterior, 

 near the center of the disk. Another conspicuous and im- 

 portant feature is the so-called liver, consisting of a pair 



